In recent time, various types of flat panel display devices capable of reducing weights and volumes, which are disadvantages of a cathode ray tube, are being developed. Examples of the flat panel display device include a liquid crystal display (LCD) device, a field emission display device, a plasma display panel, an organic light emitting display device, and the like.
Among those flat panel display devices, the plasma display device is focused on as a display device, which is light, thin, short and small and the most advantageous for providing a large-scaled screen, by virtue of simplified structure and fabricating processes. However, the plasma display device also has disadvantages in view of low luminous efficiency and brightness and high power consumption. On the other hand, the LCD device has disadvantages in view of being difficult to implement a large screen due to the use of a semiconductor process and causing high power consumption due to a backlight unit. Also, the LCD device exhibits a great optical loss and a narrow viewing angle due to optical elements, such as a polarizing filter, a prism sheet, a diffusion plate and the like.
On the contrary, light emitting display devices are classified into an inorganic light emitting display device and an organic light emitting display device according to a material of a light emitting layer. The organic light emitting display device is a self-light emitting device, which has great advantages in the aspects of fast response speed, high luminous efficiency, high brightness, and a large viewing angle. The inorganic light emitting display device causes high power consumption and is unable to obtain high brightness, as compared with the organic light emitting display device. Also, the inorganic light emitting display device cannot emit light with various colors of red (R), green (G) and blue (B). On the other hand, the organic light emitting display device is actively being studied by virtue of several advantages, such as being able to be driven by a low DC voltage, which is several tens of volts, having a fast response speed, providing high brightness, and emitting various colors of R, G and B.
Meanwhile, a flexible display device using a flexible substrate, such as a plastic substrate, has been proposed for portability and convenience in use. The flexible display device may be fabricated in such a manner of attaching a plastic substrate, such as polyimide, onto a mother substrate made of glass, forming a plurality of display panels on the mother substrate through various processes, such as a thin film transistor (TFT) process, and cutting the mother substrate into display panel units.
Typically, for a general display device, namely, for an unbendable hard display device, various components, such as a TFT, lines, and the like, are formed directly on the glass mother substrate. Hence, the mother substrate has been divided into the display panel units in such a manner of forming cutting lines, as perpendicular cracks on the mother substrate using a cutting wheel, and applying pressure onto the cutting lines to propagate the perpendicular cracks from an upper surface to a lower surface of the mother substrate.
However, the flexible display device is fabricated by attaching the plastic substrate, such as polyimide, onto the mother substrate. Accordingly, when the mother substrate is cut using the cutting wheel, the plastic substrate and the glass substrate should be cut at once. However, the plastic substrate is not easily cut by the cutting wheel due to its low hardness compared to the glass substrate. In addition, unlike cutting the general display device, for cutting the flexible display device, an increase in a thickness of an object which is to be cut may be caused due to the plastic substrate. Consequently, the perpendicular crack generated by the cutting wheel may not be completely generated on the glass substrate. This may result in the generation of a defect on a cut surface upon cutting the mother substrate.
In addition, for an organic light emitting display (OLED) device, by introduction of impurities such as moisture or air, the OLED device may be defective and reduced in lifespan. Accordingly, various types of insulating layers are formed on an entire mother substrate for preventing the introduction of foreign materials or moisture. When the mother substrate is incompletely cut by the cutting wheel, a crack is propagated along the insulating layers through the cut surface. The propagated crack serves as a path through which the foreign materials or moisture are introduced into the OLED device, thereby causing a fabrication of a defective OLED device and a reduction of a lifespan of the OLED device.